Automobile seats typically include a seat portion and a back portion molded of flexible urethane foam material. A typical process used in molding these seating foam buns is by pouring urethane precursors into an open mold and then closing the mold to allow foaming reaction and curing of the foam bun. During the foaming reaction, urethane precursors react to expand into a cellulosic structure filling the mold cavity while exhausting the air inside the mold cavity to the outside atmosphere at the same time. The evacuation of air entrapped in the mold cavity is an important step of the foam bun manufacturing process. Without an efficient air venting method, foam buns having voids and non-uniform density distribution are produced which must be scraped.
Traditionally, entrapped air in a mold cavity is evacuated to the outside atmosphere through vent holes drilled at predetermined locations in the mold. These vent holes are of a very small diameter, i.e. between 1/32 and 1/16 in., and must be strategically located such that efficient air evacuation may occur. Vent holes not placed at the correct location often lead to imperfections in the foam bun such as voids and air bubbles. The size of the vent holes are also critical since they must be large enough to allow rapid evacuation of air and small enough such that no significant amount of foam material may escape to the outside of the mold. Mold venting has been largely a trial-and-error technique which requires many tedious steps of drilling holes of different diameters at different locations before an optimum combination of vent hole locations and vent hole diameters could be found.
Moreover, when small vent holes are used, urethane foam flows into the vent holes forming flash both inside and outside the hole. The formation of urethane foam flash outside the mold sometimes is referred to as vent buns in the shape of a mushroom. These excess foam flash must be removed from the surface of the foam bun after molding which requires extensive labor. As a consequence, these vent holes must be cleaned frequently to remove foam material plugging the vent holes. More labor is involved in cleaning vent holes and spraying mold released into the vent holes to facilitate removal of foam flash.
It is, therefore, an object of the present invention to provide a foam mold equipped with a single self-cleaning mold vent assembly such that a large number of vent holes need not be drilled into the mold.
It is another object of the present invention to provide a foam mold equipped with a self-cleaning mold vent assembly which allows rapid evacuation of entrapped air in the mold cavity.
It is a further object of the present invention to provide a foam mold equipped with a mold vent assembly which does not require any cleaning process after each molding operation.